Inks for use in ink-jet printers require properties such as, for example, smear resistance, quick drying, scratch resistance and the ability to pass through an ink-jet nozzle without clogging. Preferably, the ink uses solvents that does not pose safety or environmental hazards. Accordingly, water-based inks are in particular demand. Some attempts to formulate water-based inks that satisfy the requirements of an ink-jet ink can be found in the patent literature.
U.S. Pat. No. 5,889,083 discloses an ink comprising about 40-80% water, about 0.1-10% colorant that may include carbon black, about 1-40% water-soluble or water-dispersible binder resin having a molecular weight of about 1500 to about 50000 and about 20-500 acid number as exemplified by acrylic copolymer and styrene-maleic anhydride resins, about 0.03-30% wax that can be emulsified, suspended or dispersed in water, about 0.1-10% organic solvents to increase the dispersibility of the resin or the colorant, about 0.01-5% defoamer and ammonium hydroxide to neutralize the resin and as a conductivity or pH adjusting agent.
U.S. Pat. No. 5,883,157 discloses an ink comprising water, a coloring material, a water-soluble organic solvent, about 0.01 to 5% of a 1000 to 10000 molecular weight copolymer containing sufficient carboxylic groups to provide a acid value of 50 to 700 and 0.001 to 5% of a surface active agent, wherein the foaming surface viscosity of the ink is 0.05 to 1.0 g/s.
U.S. Pat. No. 5,221,334 discloses an ink comprising an aqueous carrier, preferably having a polyhydric alcohol component, a pigment stabilized by an AB or BAB block copolymer, wherein A is a hydrophobic acrylate or methyacrylate ester, amide or nitrile, and B is a hydrophilic acrylate or methacrylate acid, ester or amide neutralized by KOH or dimethylethanolamine and a surfactant.
In the prior art discussed above, the solvents used, such as polyalcohols or sulfur and/or nitrogen containing solvents, may pose safety or environmental hazards. It would be desirable to achieve optimal ink-jet ink properties with an environmentally friendlier solvent system.
An ink composition suitable for use in ink-jet printers comprising an ethanol-water vehicle, a dispersant resin solublized by ammonium hydroxide, a translucent acrylate emulsion or a hyperdispersant, a pigment and a defoamer has been developed. The ink is stable in storage, water fast after printing, scratch resistant with high gloss, has a neutral pH, and has a low viscosity.